The present invention relates generally to minimizing impedance in capacitors and more particularly to low resistance, low inductance capacitors having a standardized outside configuration.
All capacitors have series equivalent circuits with impedance consisting of capacitance, resistance, and inductance parameters, and conventional electrolytic capacitors have resonant frequencies between 5 and 100 kilohertz depending on size, voltage rating, and construction. At frequencies below the resonant frequency, the capacitor impedance is primarily capacitive and is minimized by maximizing capacitance. While the total resistance effect, or equivalent series resistance (ESR), has minimal influence on the impedance except at frequencies near the resonant frequency, the effect of ESR is noticeable in heat generation at all frequencies. The effect of the ESR is minimized by minimizing the ESR. Above the resonant frequency, the capacitor impedance is primarily affected by the total inductance, or equivalent series inductance (ESL) and is minimized by minimizing the ESL.
In the past, the capacitors used in conventional D.C. power supplies, which rectified 60 hertz line voltage to supply the desired D.C. level operated in ranges below the resonant frequency and the effects of the ESR and ESL were minimal. With the increased acceptance of switching regulated D.C. power supplies which operate at frequencies between 10 and 100 kilohertz (with resulting 20 to 200 kilohertz ripple and harmonics), new low ESR and ESL capacitors are required because normal operation is in ranges at or above the resonant frequencies. At the same time, certain outside configurations for capacitors have become accepted in the industry such that the low ESR and ESL must be obtained without any changes to the outside configuration.
Various other capacitors have been developed having relatively low ESL's such as those shown in the Puppolo, et al., U.S. Pat. No. 3,822,397 and the Voyles, et al., U.S. Pat. No. 3,806,770. However, the split terminal cover design of the Puppolo patent and the tantalum capacitor design of the Voyles patent are expensive to manufacture.